Apparatus and a method for controlling fuel supply to engine

ABSTRACT

A basic discharge QK Of a fuel pump is determined based on an engine load and an engine rotational speed, and further a correction amount QG for correcting the basic discharge QK based on comparison of an actual fuel pressure PT with a target pressure Po is learnt for every driving conditions. Then, the basic discharge QK is corrected with the correction amount QG, whereas in a transient condition, the basic discharge QK is corrected with a transient correction amount QT set on the basis of a variation rate ΔPT Of the fuel pressure PT. Thus, it is possible to ensure that an amount of fuel required by an engine is surely supplied without excess fuel supply from the fuel pump.

TECHNICAL FIELD

The present invention relates to an apparatus and a method forcontrolling fuel supply to an engine, and more particularly to atechnique for controlling the operation of a fuel pump for force-feedingfuel to the engine, in accordance with an amount of fuel required by theengine.

BACKGROUND ART

The electronically controlled fuel injection system has conventionallycontrolled an amount of fuel to be supplied to an engine by controllingvalve opening time of a fuel injection valve.

In such a conventional fuel injection system, it is impossible to injecta constant amount of fuel in accordance with the valve opening time,unless a differential pressure is kept to be constant between thepressure of fuel to be supplied to the fuel injection valve and theintake pressure in the vicinity of an injection hole of the fuelinjection valve.

Accordingly, there has conventionally been provided a pressure regulatorfor controlling the pressure of fuel to be supplied to a fuel injectionvalve from a fuel pump, and to a reference pressure chamber of thepressure regulator has been introduced the inlet negative pressure fromthe downstream of a throttle valve. If a differential pressure betweenthe pressure in the reference pressure chamber and the pressure of fuelsupplied from the fuel pump exceeds a predetermined value, a returnpassage is forced to open for returning fuel to the fuel pump to therebykeep the differential pressure to be constant (See Japanese UnexaminedPatent Publication No. 60-212634).

In such an apparatus as above mentioned in which the pressure of fuel tobe supplied to a fuel injection valve is controlled by adjusting anamount of fuel which is returned by the pressure regulator, the fuelpump is controlled to discharge a slight larger amount of fuel thanrequired for maintaining the aforementioned differential pressure to beconstant even if an amount of fuel required by an engine increase.Therefore, a slight amount of fuel required by an engine has resultedthat much of fuel is returned back to a fuel tank as return fuel.

The return fuel brought back to the fuel tank from the pressureregulator is warmed up by heat generated by the engine. Accordingly, thetemperature of fuel contained in the fuel tank is increased by thewarmed return fuel, and hence there are generated fuel vapors in thefuel tank. Thus, it has been desired to reduce an amount of return fuelas much as possible.

Thus, it has been suggested to control discharge of a fuel pump inaccordance with an amount of fuel required by an engine. However, inthis suggestion, it has been necessary to control the fuel pump so thatthe pump discharges a little larger amount of fuel than required, so asto disregard the dispersion and variation in discharge of a fuel pump,with the result of generation of return fuel.

Another system has been proposed for avoiding the generation of returnfuel. In this system , there is provided a sensor for detecting thepressure of fuel present in a fuel supply passage, and the discharge ofa fuel pump is controlled in accordance with the fuel pressure detectedby the sensor.

However, in such a system as above mentioned in which the detected fuelpressure is fed back to control discharge of a fuel pump, for instance,during transition period in which a required fuel amount isincrementally changed, the discharge of the fuel pump is controlled toincrease after the fuel pressure has been decreased as the required fuelamount is incrementally changed. This brings the result that the fuelpressure decreases due to response delay in control and also due tosupply delay of fuel, and hence an amount of fuel required by an enginemay not be supplied quite precisely during transient driving.

The invention aims to overcome the aforementioned problems, and thus itis an object of the present invention to provide a system in which it ispossible to prevent generation of return fuel causing the temperaturerise in a fuel tank, and also possible to securely force-feed a requiredamount of fuel even if discharge of a fuel pump is varied due to thevariation and/or degradation of the fuel pump.

Another object of the present invention is to make it possible toaccomplish a correction control with high accuracy in order tocompensate for the variation in discharge of the fuel pump generated dueto the variation and/or degradation of the fuel pump.

A further object of the present invention is to make it possible tosecure the follow up to the fuel pressure during transient driving,while preventing generation of the return fuel.

DISCLOSURE OF THE INVENTION

In order to overcome the aforementioned problems, the present inventionis constructed so that a basic control value for a fuel pump is set inaccordance with an engine driving condition, the pressure of fuelforce-fed from the fuel pump is detected, a correction value is learnedfor every driving conditions in order to correct the basic control valuein accordance with comparison of the detected fuel pressure with atarget pressure, and the fuel pump is controlled to drive in accordancewith a final control value obtained by correcting the basic controlvalue with the correction value.

According to such a construction, even if the correlation between thecontrol value and the discharge or fuel pressure of the fuel pump isvaried due to the variation and/or degradation of individual fuel pumps,the control value is corrected to thereby obtain a target pressure.Thus, it is possible to supply an optimum amount of fuel through thefuel pump, while preventing excessive fuel supply.

In another aspect, the invention is constructed so that a variation ratein an amount of fuel required by the engine is detected, and then thebasic control value is corrected in accordance with the variation rate,and thus the fuel pump is controlled to drive in accordance with thethus corrected basic control value.

According to this construction, even when the amount of fuel required bythe engine is varied, and hence response delay may occur if the fuelpump is controlled to drive in accordance with the basic control value,it is possible to avoid the response delay by the correction made inaccordance with the variation rate. Thus, it is possible to secure theoptimum amount of fuel even when the amount of fuel required by anengine is varied, while preventing excessive fuel supply in steadydriving condition.

It is preferable to use the engine load and the rotational speed ofengine as an engine driving condition for setting the basic controlvalue.

Namely, since the required amount of fuel per a unit rotation can bedetermined based on the engine load, it is possible to assume the amountof fuel required by the engine per a unit period of time based on theengine load and the rotational speed of engine.

It is preferable to detect one of variations in the pressure of fuelforce-fed from the fuel pump, in an amount of intake air supplied intothe engine, and in basic injection pulse width of a fuel injection valvecalculated in accordance with an amount of intake air supplied to acylinder, as a parameter representing the variation rate of the amountof fuel required by the engine.

Namely, when the fuel pressure is varied in a great degree, it ispossible to assume that the response delay is increased accordingly ifthe fuel pump is controlled only in accordance with the basic controlvalue. In addition, both the variations in the intake air amount to besupplied to the engine and in basic injection pulse width correspond tothe variation in the amount of fuel required by the engine. Thus it ispossible to make a correction in accordance with the required fuelamount by setting a transient correction value according to theparameter.

It is preferable to learn the correction value in accordance withcomparison of the pressure of fuel force-fed from the fuel pump with thetarget pressure under the condition that the engine is in steady drivingoperation.

It is possible to detect an error of the basic control value with highaccuracy by permitting to learn the correction value only when theengine is in steady driving condition.

When the correction value is learnt in accordance with comparison of thepressure of fuel force-fed from the fuel pump with the target pressure,it is preferable to newly calculate a correction value based on thedetected pressure, the target pressure and the basic control value atthe time, and then renew stored data using a weighted mean value of thenewly calculated correction value and the previous correction value as acorrection value for the driving condition.

By using the weighted mean value of the previous learnt value and thenewly learnt value, it is possible to avoid falsely learning due to anunexpected variation in pressure and setting a correction value quitedifferently from a required level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing basic elements for constituting thepresent invention as recited in claim 1.

FIG. 2 is a block diagram showing basic elements for constituting thepresent invention as recited in claim 2.

FIG. 3 is a schematic system diagram illustrating an embodiment inaccordance with the present invention.

FIG. 4 is a flow chart showing how a fuel pump is controlled to drive inthe embodiment.

FIG. 5 is a flow chart showing how a correction value is learnt forevery driving conditions in the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow will be explained an embodiment in accordance with thepresent invention.

In FIG. 3 illustrating an embodiment in accordance with the presentinvention, fuel contained in a fuel tank 1 is sucked by a fuel pump 2,and then discharged therefrom to be force-fed to a plurality of fuelinjection valves 4 through a fuel supply passage 3.

The fuel injection valves 4 are of electromagnetic type fuel injectionvalves which are made open when an electrical current is applied to asolenoid, while closed when an electrical current is not applied to asolenoid. The fuel injection valves 4 are controlled to intermittentlyopen in accordance with drive pulse signals of a predetermined pulsewidth Ti (a valve opening time) which is transmitted from a control unit7 to be described later and corresponds to an amount of fuel required byan engine, and thus inject fuel into an intake air passage disposeddownstream of a throttle valve of the engine (not illustrated).

In the fuel supply passage 3 is disposed a fuel filter 5 and serving asa fuel pressure detecting means a fuel pressure sensor 6 for detectingfuel pressure PT in the vicinity of the fuel injection valves 4. Thefuel pressure PT detected by the fuel pressure sensor 6 is transmittedto the control unit 7 which controls the operation of the fuel pump 2.

Into the control unit 7 are transmitted a detecting signal from the fuelpressure sensor 6, an intake air flow detecting signal Q from an airflow meter 8, and a rotational speed signal Ne from a crank angle sensor9.

The control unit 7 having therein a microcomputer calculates a basicinjection pulse width Tp (or a basic valve opening time) correspondingto an amount of fuel required by the engine, based on the intake airflow Q and the rotational speed Ne, and also sets various correctioncoefficients COEF in accordance with data such as a temperature Tw ofcooling water and the like. Then, the control unit 7 corrects the basicinjection pulse width Tp with the correction coefficients COEF tothereby set a final injection pulse width Ti.

The control unit 7 outputs a drive pulse signal having theaforementioned injection pulse width Ti to the fuel injection valves ata predetermined timing to thereby intermittently supply fuelcorresponding to the required amount to the engine in accordance with avalve opening time.

In order to control the fuel amount injected from the fuel injectionvalves 4 in accordance with the valve opening time, it is necessary tocontrol the fuel pressure PT SO as to be coincident with a targetpressure (namely, a fuel pressure at which a differential pressurebetween an intake negative pressure of the engine and the fuel pressureis constant) corresponding to the driving condition (the intake negativepressure of the engine). To this end, the control unit 7 determines arequired discharge (a control value) of the fuel pump 2 as shown in theflow chart in FIG. 4, to thereby control a voltage (or ON/OFF controlduty) to be applied to the fuel pump 2 in accordance with the thusdetermined discharge.

It should be noted in the embodiment that the control unit 7 hasfunctions of basic control value storing means, correction valuelearning means and fuel pump control means as recited in claim 1 (SeeFIG. 1 ), and also has functions of basic control value storing means,required amount variation rate detecting means, transient correctionvalue setting means and fuel pump control means as recited in claim 2(See FIG. 2), as shown in the flow chart in FIG. 4.

It also should be noted that driving condition detecting means asrecited in claims 1 and 2 (See FIGS. 1 and 2) are embodied as the airflow meter 8 and the crank angle sensor 9 respectively.

In the flow chart in FIG. 4, a basic discharge QK corresponding to theengine driving condition at the present time is retrieved in step 1 withreference to a map storing therein a basic discharge QK (a basic controlvalue) required by the fuel pump 2 during steady driving for each of aplurality of driving areas divided in dependence on the injection pulsewidth Ti (a value corresponding to the engine load) and the enginerotational speed Ne.

The basic discharge QK means a discharge by which the fuel pressure PTcan be arranged to be coincident with a target pressure corresponding tothe driving condition (an intake negative pressure of the engine) on theassumption that there is no variation or degradation of the fuel pump 2.The basic discharge QK is determined in advance by experiments, and isstored in the map.

In step 2, if a desired discharge cannot be obtained due to thevariation and/or degradation of the fuel pump 2, a learnt correctionamount QG (a learnt correction value) learnt for compensating for excessand shortage of the discharge is retrieved. The learnt correction amountQG is stored so that it can be reloaded in the map in dependence on theinjection pulse width Ti and the rotational speed Ne, similarly to thebasic discharge QK. The learnt correction amount QG corresponding to thedriving condition at the present time can be retrieved by referring tothe map.

How the learnt correction amount QG is set by learning will be explainedlater.

In step 3, it is judged as to whether or not the driving condition is atransient condition in which the amount of fuel required by the enginevaries, based on the variations, for example, in the fuel pressure PT,the intake air flow Q, and the basic injection pulse width Tp.

If the judgment indicates that the driving condition is not a transientcondition, a final discharge QF (←QK+QG) is calculated in step 4 basedon the basic discharge QK and the learnt correction amount QG.

Then, control proceeds from step 4 to step 7, the discharge QF (thefinal control value) is converted to a control output such as a voltageto be applied to the fuel pump 2. The fuel pump 2 receives the thusconverted control output, and is controlled to drive in accordance withthe output.

On the other hand, if the judgment in step 3 indicates that the drivingcondition is a transient condition, control proceeds to step 5 wherein atransient correction amount QT (a transient correction value) forcompensating for a response delay generated due to a fuel feeding timeduring transition period is set on the basis of a variation rate (atransient variation rate) of parameters correlating to enginerequirements such as the fuel pressure PT, the intake air flow Q and thebasic injection pulse width Tp.

It is desirable to provide in advance a map storing transient correctionamounts QT corresponding to the variation rates ΔPT, AQ and ΔTp of thefuel pressure PT, the intake air flow Q and the basic injection pulsewidth Tp respectively, and thus to make it possible to set the transientcorrection amount QT by referring to the map.

In step 6, the final discharge QF (←(QK+QG)×QT)is calculated on thebasis of the basic discharge QK, the learnt correction amount QG and thetransient correction amount QT.

In accordance with the foregoing embodiment, the basic discharge QK isstored in advance based on the injection pulse width Ti and the enginerotational speed Ne to thereby ensure that the discharge correspondingto the engine driving condition at the time can be obtained without aresponse delay from a viewing point of control.

The discharge QF determined as QF (←QK+QG) is able to maintain thedesired fuel pressure PT during steady driving condition in which theamount of fuel required by the engine is approximately constant.However, when the required fuel amount changes to increase, forinstance, the fuel pressure PT is reduced due to a feed delay of fueleven if the discharge is controlled to correspond to the increase of therequired fuel amount.

Thus, the discharge QF is corrected in the transient condition inaccordance with the transient variation rate of the fuel amount requiredby the engine, to thereby make it possible to correct the responsedelay.

Hereinbelow will be explained how the learnt correction amount QG iscontrolled to be set by learning with reference to the flow chart shownin FIG. 5. It should be noted that the function of the control unit 7shown in the flow chart in FIG. 5 corresponds to correction valuelearning means as recited in claim 1.

In step 11 in the flow chart of FIG. 5, it is judged as to whether alearning condition is established or not. The learning condition meansthe steady condition in which the engine rotational speed Ne, the basicinjection pulse width Tp, the fuel pressure PT and the opening degree ofthe throttle valve TVO are approximately constant.

When the learning condition is established, a new learnt correctionamount QG is calculated in accordance with the following equation.

    QG←QK-QK×1/(Po/PT)1/2

In the above equation, Po represents a target value for the fuelpressure in the driving condition at the present time. By theequation,excess and shortage of basic discharge QK is newly establishedas the learnt correction amount QG, in accordance with a ratio of thetarget pressure Po to an actually detected fuel pressure PT.

In step 13, by referring to a map storing learnt correction amounts QGin accordance with the injection pulse width Ti (a value equivalent tothe engine load) and the engine rotational speed Ne, the learntcorrection amount QG stored in the map correspondingly to the drivingcondition is retrieved as the pre-renewed learnt correction amount QG₋₁.

Then, in step 14, a weighted mean of the learnt correction amount QGnewly calculated in step 12 and the previous or pre-renewed learntcorrection amount QG₋₁ retrieved in step 13 is calculated, and the thuscalculated weighted mean is set as a map renewal value QGnew.

In step 15, the map renewal value QGnew is reloaded in the map of thelearnt correction amount QG as data corresponding to the present drivingcondition.

Thus, when the fuel pump 2 is controlled to drive in accordance with thebasic discharge QK which is set so as to obtain the target pressure Po,the learnt correction amount QG corresponding to excess and shortage ofthe basic discharge QK is learnt to be set for every driving conditionsbased on comparison of the target pressure Po with the actual fuelpressure PT, if the target pressure Po cannot actually be obtained.

Thus, even if the discharge (fuel pressure) obtained correspondingly tothe control output is different from an expected value due to thevariation and/or degradation of the fuel pump 2, such a difference canbe compensated to thereby ensure a desired discharge. In addition, it ispossible to enhance accuracy of discharge control for the fuel pump 2accomplished in dependence on the injection pulse width Ti and theengine rotational speed Ne, and also possible to obtain an optimum fuelpressure with high accuracy for every driving conditions withoutgeneration of excess fuel.

In the above mentioned embodiment, the basic discharge QK and the learntcorrection amount QG are stored in dependence on the injection pulsewidth Ti and the engine rotational speed Ne. However, it should be notedthat if the engine is of type having a boost sensor in place of the airflow meter 8, an intake negative pressure detected by the boost sensormay be used as a parameter corresponding to the engine load in place ofthe injection pulse width Ti.

INDUSTRIAL APPLICABILITY

As aforementioned, in accordance with the apparatus and method forcontrolling fuel supply to the engine according to the presentinvention, in a construction wherein fuel is force-fed to a fuelinjection valve through a fuel pump, a required fuel amount can beensured without excess fuel supply from the fuel pump. The applicationof the apparatus and method to an engine for an automobile ensures toavoid the temperature rise in a fuel tank due to return fuel back fromthe engine, thereby it is possible to provide an automobile capable ofavoiding diffusion of fuel into atmosphere.

We claim:
 1. An apparatus for controlling fuel supply to an engine,comprising:a fuel injection valve for injecting fuel therethrough intoan intake system of said engine; a fuel pump for sucking thereinto fuelcontained in a fuel tank and force feeding the fuel to said fuelinjection valve through a fuel supply passage; driving conditiondetecting means for detecting a driving condition of said engine,correlating to an amount of fuel required by said engine; control valuefor steady condition setting means for setting a control value forsteady condition for said fuel pump, corresponding to a steadycondition, said control value for steady condition being determinedusing said driving condition of said engine detected by said drivingcondition detecting means as a parameter; transient condition detectingmeans for detecting a transient condition where said amount of fuelrequired by said engine varies, and for detecting a variation rate ofsaid amount of fuel required by said engine; transient correction valuesetting means for setting a transient correction value for correctingsaid control value for steady condition based on said variation rate ofsaid required fuel amount detected by said transient condition detectingmeans; and fuel pump control means for setting a final control value bycorrecting said control value for steady condition based on saidtransient correction value when the transient condition is detected bysaid transient condition detecting means, while setting said controlvalue for steady condition as a final control value when a transientcondition is not detected by said transient condition detecting means,and for controlling and driving said fuel pump based on a thus set finalcontrol value.
 2. An apparatus for controlling fuel supply to an engineas claimed in claim 1, wherein said control value for steady conditionsetting means comprises:basic control value storing means for storing inadvance a basic control value for said fuel pump, said basic controlvalue being determined using said driving condition of said enginedetected by said driving condition detecting means as a parameter; fuelpressure detecting means for detecting the pressure of fuel force-fedfrom said fuel pump; correction value learning means for learning acorrection value for correcting said basic control value based oncomparison of the fuel pressure detected by said fuel pressure detectingmeans with a target pressure, and for storing thus learnt correctionvalue for every engine driving condition detected by said drivingcondition detecting means; and basic control value correcting means fordetermining a basic control value and a correction value bothcorresponding to the engine driving condition detected by said drivingcondition detecting means by said basic control value storing means andsaid correction value learning means, and for setting a value obtainedby correcting said basic control value based on said correction value asa final control value for steady condition.
 3. An apparatus forcontrolling fuel supply to an engine as claimed in claim 1, wherein saiddriving condition detecting means detects engine load and enginerotational speed.
 4. An apparatus for controlling fuel supply to anengine as claimed in claim 1, wherein said transient condition detectingmeans detects a variation rate of one of parameters of the pressure offuel force-fed from said fuel pump, an amount of intake air suppliedinto said engine, and basic injection pulse width of said fuel injectionvalve, and detects a transient condition based on the detected variationrate.
 5. An apparatus for controlling fuel supply to an engine asclaimed in claim 2, wherein said correction value learning means learnsa correction value only under the condition of steady driving conditionof said engine.
 6. An apparatus for controlling fuel supply to an engineas claimed in claim 2, wherein said correction value learning meanscalculates a new correction value based on the detected fuel pressure,the target pressure, and the basic control value stored in said basiccontrol value storing means corresponding to the engine drivingcondition at the time, and reloads data using a weighted means value ofthe correction value stored corresponding to the engine drivingcondition at the time and said correction value newly calculated, as acorrection value corresponding to said engine driving condition.
 7. Amethod for controlling fuel supply to an engine having a fuel injectionvalve for injecting fuel therethrough into an intake system of saidengine, and a fuel pump for sucking thereinto fuel contained in a fueltank and force-feeding said fuel to said fuel injection valve through afuel supply passage, said method comprising the steps of:detecting anengine driving condition correlating to an amount of fuel required bysaid engine; setting a control value for steady condition for said fuelpump corresponding to a steady condition, said control value for steadycondition being determined using said driving condition of said enginedetected in said step of detecting an engine driving condition;detecting a transient condition where said amount of fuel required bysaid engine varies, and detecting a variation of said amount of fuelrequired by said engine; setting a transient correction value forcorrecting said control value for steady condition based on saidvariation rate of said required fuel amount detected in said step ofdetecting a transient condition; and setting a final control value bycorrecting said control value for steady condition based on saidtransient correction value when a transient condition is detected insaid step of detecting a transient condition, while setting said controlvalue for steady condition as a final control value when a transientcondition is not detected in said step of detecting a transientcondition, and controlling and driving said fuel pump based on a thusset final control value.
 8. A method for controlling fuel supply to anengine as claimed in claim 7, wherein said step of setting a controlvalue for steady condition comprises the steps of:storing in advance abasic control value for said fuel pump, said basic control value beingdetermined using said driving condition of said engine detected in saidstep of detecting a driving condition as a parameter; detecting thepressure of fuel force-fed from said fuel pump; learning a correctionvalue for correcting said basic control value based on comparison of thefuel pressure detected in said step of detecting the fuel pressure witha target pressure, and storing thus learnt correction value for everyengine driving condition detected in said step of detecting a drivingcondition; and determining a basic control value and a correction valueboth corresponding to the engine driving condition detected in said stepof detecting a driving condition and said step of storing a basiccontrol value and said step of learning a correction value, and settinga value obtained by correcting said basic control value based on saidcorrection value as a final control value for steady condition.
 9. Amethod for controlling fuel supply to an engine as claimed in claim 7,wherein said step of detecting an engine driving condition includesdetecting the engine load and the engine rotational speed.
 10. A methodfor controlling fuel supply to an engine as claimed in claim 7, whereinsaid step of detecting a transient condition includes detecting avariation rate of one of parameters of the pressure of fuel force-fedfrom said fuel pump, an amount of intake air supplied into said engine,and basic injection pulse width of said fuel injection valve, anddetecting a transient condition based on the detected variation rate.11. A method for controlling fuel supply to an engine as claimed inclaim 8, wherein said step of learning a correction value includeslearning a correction value only under the condition of steady drivingcondition of said engine.
 12. A method for controlling fuel supply to anengine as claimed in claim 8, wherein said step of learning a correctionvalue includes calculating a new correction value based on the detectedfuel pressure, the target pressure, and the basic control value storedin said basic control value storing step corresponding to the enginedriving condition at the time, and reloading data using a weighted meansvalue of the correction value stored corresponding to the engine drivingcondition at the time and said correction value newly calculated, as acorrection value corresponding to said engine driving condition.